[PPC] Fix cpm_dpram_addr returning phys mem instead of virt mem

cpm_dpram_addr returns physical memory of the DP RAM instead of
iomapped virtual memory. As there usually is a 1:1 MMU map of
the IMMR area, this is often not noticed. However, cpm_dpram_phys
assumes this iomapped virtual memory and returns garbage on the
1:1 mapped memory causing CPM1 uart console to fail.

This patch fixes the problem (copied from the powerpc tree).

Signed-off-by: Jochen Friedrich <jochen@scram.de>